An ink-jet printer is a type of non-impact printer which forms characters and other images by controllably spraying drops of ink from a printhead. One conventional type of ink-jet printhead consists of a replaceable cartridge or pen which is mounted to a movable carriage. The pen controllably ejects liquid ink through multiple nozzles in the form of annular drops which travel across a small air gap and land on a recording media. The ink drops dry shortly thereafter to form in combination the desired printed images.
One problem associated with ink-jet printers concerns the amount of ink deposited from the pen during the formation of each drop. The quantity of deposited ink, commonly referred to as the "drop-volume" of the pen; can vary significantly from pen to pen. This wide variation in drop-volume detrimentally impacts print quality, ink dry time, and pen life. In general, variations in pen drop-volumes are caused by tolerances inherent in manufacturing or other pen characteristics. On the other hand, for any given pen, the drop-volume remains fairly constant over the majority of the life of that pen. Accordingly, it would be desirable to develop a technique for detecting the drop-volumes of different pens.
One prior approach to solving the above problem is simply to produce pens according to tighter manufacturing tolerances. Pens with higher precision specifications tend to have more consistent drop-volumes. Unfortunately, this approach involves expensive manufacturing equipment, thereby driving up the production cost of such pens.
Another proposed solution involves computing drop-volume by measuring the optical density of a solid printed area of ink. It is difficult, however, to obtain a precise reading of drop-volume from optical density because there is substantial variability in the measurement. The optical density of the printed solid area is dependent on other factors apart from drop-volume, such as the recording media and ink, and thus is less effective at isolating and deriving the pen drop-volume.
A related approach is to print a line of single ink drops and measure its width. Pens having a comparatively high drop-volume would produce a wider line, whereas pens having a comparatively low drop-volume would yield a narrower line. This measurement, however, tends to be noisy and often fails to produce repeatable results.
Another prior technique involves deducing drop-volume by measuring the mass of the ink drops ejected from the pen. This technique has a drawback in that it requires expensive equipment, such as a precision balance, to accurately weigh ink drops. Additionally, the technique is time-consuming and not suitable for automation into a high-speed manufacturing environment. As a result, the method cannot practically be implemented in the manufacturing of low-cost ink-jet printers.
None of the above prior solutions have proven effective for providing a low-cost approach to accurately determining drop-volume of ink-jet pens. Accordingly, it is an objective of this invention to provide a method for detecting nominal drop-volume of a pen. It is also an objective to compensate for various pen drop-volumes to yield more consistent print quality, ink dry time, and pen life.